Monoamine oxidase (MAO, E.C. 1.4.3.4) is primarily responsible for the degradation of amine transmitters in the nervous system; levels of enzyme activity can affect several parameters of neurologic function in humans and experimental animals. Our studies are designed to elucidate the structure of the two forms of this enzyme, MAO-A and MAO-B, and the regulation of their activity using techniques of cell culture, biochemistry, somatic cell genetics and molecular biology. Active MAO molecules in living cells or homogenates will be tagged specifically and irreversibly with 3H-pargyline or a fluorescein-conjugated pargyline derivative. MAO-A and MAO-B molecules from different species will be distinguished by two-dimensional gel electrophoresis and quantified by binding assays. Cells with without MAO-A and MAO-B will be screened by replica plating and autoradiography, or by fluorescence microscopy and the use of fluorescence activated cell sorter. We will: 1) determine the number of genes involved in expression of MAO activity and establish whether any of these genes are unique to MAO-A or MAO-B by obtaining mutants lacking activity; 2) map he chormosomal location of the human gene coding for the flavin-containing subunit of MAO-B and establish its position relative to that for MAO-A; 3) identify fragments of human genomic DNA containing the gene for MAO be gene transfer; and 4) determine how hormones induce changes in MAO-A and MAO-B activities.